Glass drawing tank



April 4 1939- w, o. AMsLr-:R 2,153,228

GLASS DRAWING TANK Filed March 29, 1937 INVENTOR r 'b ATTORNEYS Patented Apr. 4, 1939 PATENT F F I Q E 2,153,228 amiss nnawma' 'ram Walter 0. Amster, Butler, Fa., assigner to Frazier-Simplex, Inc., a corporation oi Delaware Application March 29, 1937, Serial No. 133,523

This invention relates to tanks for' the drawing of glass in sheet form, and consists in a feature of structure that permits the doing away with an otherwise indispensible adjunct; and, l

in consequence, the structure as a whole is simplied, operation is expedited, and asource of defect is eliminated.

In the accompanying drawing Fig. I is a fragmentary view in vertical section of a tank of `mv invention, showing the glass-drawing operation in progress; Fig. II is a view in vertical section, on the plane indicated at 1lim Fig. I; and Fig. m is a View corresponding to Fig. I of a tank in which the feature that constitutes the invention is present in modied form.

Referring, iirst, to Figs. I and II, the drawing chamber of the glass-drawing tank of the invention is indicated at i. The chamber will be understood to be continuous with a melting chamber,

not shown, but lying to the right of the drawing,

chamber, as viewed in Fig. I. The tank-will be seen to be free and unobstructed, so that circulation currents, indicated by arrows, have free course.

The drawing chamber is roofed over, as indicated at 2, and through the roof a drawing opening 3 is formed. From the roof curtain'.walls 4 depend, screeningD the path of the sheet as it rises from the surface of the pool G of molten glass within the tank upward throughthe drawing opening 3. Beneath the roof and beyond the curtain walls 4 means may be provided for maintaining proper conditions of "temperature for drawing. Such temperature-maintaining means so disposed are known, and, since they form no part of this invention, they are not shown.

Through the opening 3 in the roof of the drawing tank the sheet of glass S is drawn directly from the free surface of the molten pool G. With the exception hereinafter to be described, the structure and the accessory appliances incident to the drawing of the sheet arecircumstantial tc this invention. Such details of structure and of accessory appliances are shown, merely by way of example of an operative whole.' To these particular details the invention is not limited. The glass is engaged primarily by a bait (not shown). As the sheet S rises its edges are first 4 ing and guiding rolls 8. These details of drawing apparatus are more fully described in Letters Patent No. 2,057,357, granted, on my application, October 13, 1936.

in the operation of glass-drawing apparatus such as that typically described, the glass rises in meniscus shape from the molten mass of the 5 pool and at the base of the up-drawn sheet; and, in consequence of the variability of conditions that cannot be perfectly controlled, that rising meniscus tends to shiit beneath the drawing means, this way and that, with a consequent l0 unevenness in the thickness of the developed sheet. Means are known to reduce this tendency to shift and to give greater deiiniteness of place to the meniscus. Such means are typically found in a bar of solid and refractory material, submerged `inst below the surface of the pool of molten glass and extending in the plane of and directly beneath the .path in which the drawn sheet rises. See, for example, Letters Patent l,339,229, granted, on the application of Harry G. Slinglu, May 4, i920. Such bar, cooling the molten glass as it approaches the region of the meniscus, has the effect of diminishing the fluctuation of position that has been indicated, and

of improving the uniformity of the drawn sheet.

There are inevitable disadvantages consequent on the presence of such a bar at the place indicated. It is subject to the action of the molten' glass streaming over its surfaces. There is no available material that under such conditions will not wear away. The bar, therefore, must periodically be replaced and renewed. The bar, having thus to be renewed, becomes itself an appreciable item of added expense of installation. More important by far is the delay of operation incident to replacement. And, besides, particles of the substance of the bar, so eroded away, enter into the body of' glass as the sheet forms and become blemishes in the drawn sheet.

This invention consists in the discovery that, 40

` by modification inthe structure of the walls of the drawing tank itself, the desired eect of stabilizing the meniscus at the base of the developing sheet may be gained, and such an accessory bar as has been indicated may be eliminated, and its undesired incidental bad effects avoided.

The bottom and side walls of the drawing tank include layers of material of high heat-insulating value. In the drawing. such a layer is indicated at 9. 'I'his material is relatively costly, and, so far as concerns strength and refractoriness, other .material is more suitable. Accordingly, it is usual to make these tank walls compound, and to include in their structure an inner layer l0 01'55 refractory tank block,`and an enveloping layer 9 of more highly heat-insulating character. I have found (and herein lies my invention) that by reducing the degree of heat insulation and increasing the degree of heat conductivity of the wall of the drawing chamber in the region immediately beneath and in substantially the plane of the developing sheet, the desired eect will be gained: the glass, elsewhere of the highly molten condition desired, becomes cooler as it approaches -the meniscus at the base of the developingr sheet;

and the meniscus gains stability.

In Figs. I and II I have shown a drawing chamber whose bottom wall extends in uniform horizontal plane, and whose side walls rise vertically beyond the limits of the breadth of the updrawn sheet. From the bottom and side walls the insulating layer 9 is absent throughout a narrow and suflicient interval II the insulating envelope is discontinuous in an interval that coincides with and extends substantially in the plane of the 11p-drawn sheet. It suilces that this slot extend, as shown in Fig. I, upward in the side walls, from the bottom toward, but to a limit preferably lower than, the normal level of the pool'of molten glass within the tank.

In consequence of such refinement of tankwall structure, the meniscus at the base of the developing sheet will be found to be stabilized, and the quality of the sheet such as is desired.

.In Fig. III I have shown the bottom wall of the drawing chamber of the tank to be stepped; the riser I 2 of this step to be left', free of a covering of insulation; and the vertical extent of the riser to be sufiicient, that it is exposed over an outer uninsulated area to the cooling effect of the air. This step in the bottom of the tank is not an obstruction to the free circulation of the molten glass; to the contrary, its relatively cool riser has eiect to accelerate the descending current adjacent its surface. This step is so situated that the portion of the body of -glass that is subject to its cooling effect is precisely the portion that is disposed beneath and in substantially the plane of the up-drawn sheet.' It has, however, the eiect that the meniscus at the base of the up-drawn sheet is stabilized, and the sheet is of desired quality.

I claim as my invention:

1. Inapparatus for the drawing of glass in sheet form, the combination of a tank free of interior obstruction to circulation, and means for drawing a sheet of glass vertically upward in a plane of determined position from the free surface of a pool of molten glass within the tank, the tank walls of heat-insulating character, exposed externally to the cooling efiect of the at'- mosphere, being of diminished insulating eifect in the region beneath and substantially in the,

sheet-developing plane of the aforesaid drawing means, whereby the body of glass within the tank'in the region of such plane is cooled and the meniscus that forms at the base of the developing sheet is stabilized in position. l

2. In apparatus for the drawing of glass in sheet form, the combination of a tank free of interior obstruction to circulation, and means for drawing a sheet of glass vertically upward in a plane of determined position from the free surface of a pool of molten glass within the tank, the tank walls, exposed externally to the cooling effect of the atmosphere, including in their structure alayer of heat-insulating material, the continuity of such layer being interrupted in the region beneath and substantially in the sheetdeveloping plane of the aforesaid drawing means.

3. In apparatus for the drawing of glass in sheet form, the combination of a tank free of interior obstruction to circulation, and means for drawing a sheet of glass vertically upward in a plane of determined position from the free surface of a pool of molten glass within the tank, the bottom wall of the tank being formed with a step including a riser that extends in vertical plane adjacent the sheet-developing plane of the aforesaid drawing means, the tank walls of heatinsulating character, exposed externally to the cooling eifect of the atmosphere, being of diminished insulating eiect Within the extent of said riser, whereby the molten glass within the tank is chilled in the plane of the up-drawn sheet and the meniscus that is formed at the base of the up-drawn sheet is stabilized in position.

4. A tank for the drawing of glass in .sheet form having a roof provided with a transverse slot through which the sheet is drawn, and having walls of heat-insulating character exposed externally to the cooling effect of the atmosphere, the said walls immediately beneath and substantially in the plane of the said slot in the roof being of diminished heat-insulating effect, whereby, in operation, the meniscus that forms at the base of the developing sheet is stabilized ,in position.

WALTER O. AMSLER. 

